23种设计模式-观察者模式

观察着模式

观察者模式（有时又被称为模型-视图（View）模式、源-收听者(Listener)模式或从属者模式）是软件设计模式的一种。在此种模式中，一个目标物件管理所有相依于它的观察者物件，并且在它本身的状态改变时主动发出通知。这通常透过呼叫各观察者所提供的方法来实现。此种模式通常被用来实现事件处理系统。

基本介绍

观察者模式（Observer）完美的将观察者和被观察的对象分离开。举个例子，用户界面可以作为一个观察者，业务数据是被观察者，用户界面观察业务数据的变化，发现数据变化后，就显示在界面上。面向对象设计的一个原则是：系统中的每个类将重点放在某一个功能上，而不是其他方面。一个对象只做一件事情，并且将他做好。观察者模式在模块之间划定了清晰的界限，提高了应用程序的可维护性和重用性。观察者设计模式定义了对象间的一种一对多的组合关系，以便一个对象的状态发生变化时，所有依赖于它的对象都得到通知并自动刷新。

实现方式

观察者模式有很多实现方式，从根本上说，该模式必须包含两个角色：观察者和被观察对象。在刚才的例子中，业务数据是被观察对象，用户界面是观察者。观察者和被观察者之间存在“观察”的逻辑关联，当被观察者发生改变的时候，观察者就会观察到这样的变化，并且做出相应的响应。如果在用户界面、业务数据之间使用这样的观察过程，可以确保界面和数据之间划清界限，假定应用程序的需求发生变化，需要修改界面的表现，只需要重新构建一个用户界面，业务数据不需要发生变化。

观察

实现观察者模式的时候要注意，观察者和被观察对象之间的互动关系不能体现成类之间的直接调用，否则就将使观察者和被观察对象之间紧密的耦合起来，从根本上违反面向对象的设计的原则。无论是观察者“观察”观察对象，还是被观察者将自己的改变“通知”观察者，都不应该直接调用。

实例

Java代码:

//观察者，需要用到观察者模式的类需实现此接口
public interface Observer{void update(Object...objs);
}//被观察者（一个抽象类，方便扩展）
public abstract class Observable{public final ArrayList<Class<?>> obserList = new ArrayList<Class<?>>();/**AttachObserver（通过实例注册观察者）*<b>Notice:</b>obcan'tbenull,oritwillthrowNullPointerException**/public<T> void registerObserver(T ob){if(ob==null) throw new NullPointerException();this.registerObserver(ob.getClass());}/***AttachObserver（通过Class注册观察者）*@paramcls*/public void registerObserver(Class<?> cls){if(cls==null) throw new NullPointerException();synchronized(obserList){if(!obserList.contains(cls)){obserList.add(cls);}}}/**UnattachObserver（注销观察者）*<b>Notice:</b>*<b>ItreverseswithattachObserver()method</b>**/public<T>void unRegisterObserver(Tob){if(ob==null) throw new NullPointerException();this.unRegisterObserver(ob.getClass());}/**UnattachObserver（注销观察者，有时候在未获取到实例使用）*<b>Notice:</b>*<b>ItreverseswithattachObserver()method</b>**/public void unRegisterObserver(Class<?>cls){if(cls==null) throw new NullPointerException();synchronized(obserList){Iterator<Class<?>>iterator=obserList.iterator();while(iterator.hasNext()){if(iterator.next().getName().equals(cls.getName())){iterator.remove();break;}}}}/**detachallobservers*/public void unRegisterAll(){synchronized(obserList){obserList.clear();}}/**Ruturnthesizeofobservers*/public int countObservers(){synchronized(obserList){returnobserList.size();}}/***notify all observer（通知所有观察者，在子类中实现）*@paramobjs*/public abstract void notifyObservers(Object... objs);/***notify one certain observer（通知某一个确定的观察者）*@paramcls*@paramobjs*/public abstract void notifyObserver(Class<?> cls, Object... objs);/***notifyonecertainobserver*@paramcls*@paramobjs*/public abstract<T> void notifyObserver(T t, Object... objs);
}//目标被观察者
public class ConcreteObservable extends Observable{private static ConcreteObservableinstance = null;private ConcreteObservable(){};public static synchronized ConcreteObservablegetInstance(){if(instance == null){instance=newConcreteObservable();}returninstance;}@Overridepublic <T> void notifyObserver(T t, Object... objs){if(t == null) throw new NullPointerException();this.notifyObserver(t.getClass(), objs);}@Overridepublic void notifyObservers(Object... objs){for(Class<?>cls : obserList){this.notifyObserver(cls, objs);}}//通过java反射机制实现调用@Overridepublic void notifyObserver(Class<?>cls, Object...objs){if(cls == null) throw new NullPointerException();Method[] methods = cls.getDeclaredMethods();for(Method method : methods){if(method.getName().equals("update")){try{method.invoke(cls,objs);break;}catch(IllegalArgumentException e){e.printStackTrace();}catch(IllegalAccessException e){e.printStackTrace();}catch(InvocationTargetException e){e.printStackTrace();}}}}
}//使用(实现Observer接口）
public class Text extends Activity implements Observer{publicvoidonCreate(...){ConcreteObservable.getInstance().registerObserver(Text.class);....}//实现接口处理publicvoidupdate(Object...objs){//做操作，比如更新数据，更新UI等}
}

php代码:

<?php
class car implements SplSubject
{//车的类型private $carName;//车的状态，0为关闭，1这启动车子private $carState = 0;//初始化车的速度表值private $carSpeed = 0;//各项车的性能观察对象private $Observers;public function __construct($Name){$this->carName   = $Name;$this->Observers = new SplObjectStorage;}//启动public function start(){$this->carState = 1;$this->notify();}//停车public function stop(){$this->carState = 0;$this->carSpeed = 0;$this->notify();}//加速public function accelerate($Acceleration){if (0 === $this->carState) {throw new Exception('先踩油门，不然车怎走啊!!!');}if (!is_int($Acceleration) || $Acceleration < 0) {throw new Exception('加速值错了啊');}$this->carSpeed += $Acceleration;$this->notify();}//增加监测对象public function attach(SplObserver $observer){if (!$this->Observers->contains($observer)) {$this->Observers->attach($observer);}return true;}//删除监测对象public function detach(SplObserver $observer){if (!$this->Observers->contains($observer)) {return false;}$this->Observers->detach($observer);return true;}//传送对象public function notify(){foreach ($this->Observers as $observer) {$observer->update($this);}}public function __get($Prop){switch ($Prop) {case 'STATE':return $this->carState;break;case 'SPEED':return $this->carSpeed;break;case 'NAME':return $this->carName;break;default:throw new Exception($Prop . 'cannotberead');}}public function __set($Prop, $Val){throw new Exception($Prop . 'cannotbeset');}
}class carStateObserver implements SplObserver
{private $SubjectState;public function update(SplSubject $subject){switch ($subject->STATE) {case 0:if (is_null($this->SubjectState)) {echo $subject->NAME . '没有启动呢' . "\t";} else {echo $subject->NAME . '熄火了' . "\t";}$this->SubjectState = 0;break;case 1:if (1 !== $this->SubjectState) {echo $subject->NAME . '启动了' . "\t";$this->SubjectState = 1;}break;default:throw new Exception('UnexpectederrorincarStateObserver::update()');}}
}class carSpeedObserver implements SplObserver
{public function update(SplSubject $subject){if (0 !== $subject->STATE) {echo $subject->NAME . '目前速度为' . $subject->SPEED . 'Kmh' . "\t";}}
}class carOverspeedObserver implements SplObserver
{public function update(SplSubject $subject){if ($subject->SPEED > 130) {throw new Exception('加速限制在130以内,你违规了!' . "\t");}}
}
try {$driver       = new  car('AUDIA4');$driverObserver1  = new carStateObserver;$driverObserver2  = new carSpeedObserver;$drivesrObserver3 = new carOverspeedObserver;$driver->attach($driverObserver1);$driver->attach($driverObserver2);$driver->attach($drivesrObserver3);$driver->start();$driver->accelerate(10);$driver->accelerate(30);$driver->stop();$driver->start();$driver->accelerate(50);$driver->accelerate(70);$driver->accelerate(100);$driver->accelerate(150);
}
catch (Exception $e) {echo $e->getMessage();
}
?>

C++代码:

//filename observer.h
#include <iostream>
#include <set>
#include <string>
using namespace std;
/抽象模式定义
class CObservable;
//观察者，纯虚基类
class CObserver
{
public:CObserver(){};virtual ~CObserver(){};//当被观察的目标发生变化时，通知调用该方法//来自被观察者pObs, 扩展参数为pArgvirtual void Update(CObservable* pObs, void* pArg = NULL) = 0;
};
//被观察者，即Subject
class CObservable
{
public:CObservable() : m_bChanged(false) {};virtual ~CObservable() {};void Attach(CObserver* pObs);   //注册观察者void Detach(CObserver* pObs);   //注销观察者void DetachAll();               //注销所有观察者void Notify(void* pArg = NULL); //若状态变化，则遍历观察者，逐个通知更新bool HasChanged();              //测试目标状态是否变化int GetObserversCount();        //获取观察者数量
protected:void SetChanged();              //设置状态变化!!!必须继承CObservable才能设置目标状态void ClearChanged();            //初始化目标为未变化状态
private:bool m_bChanged;                //状态set<CObserver*> m_setObs;       //set保证目标唯一性
};
/抽象模式实现
void CObservable::Attach(CObserver* pObs){if (!pObs) return;m_setObs.insert(pObs);
}
void CObservable::Detach(CObserver* pObs){if (!pObs) return;m_setObs.erase(pObs);
}
void CObservable::DetachAll(){m_setObs.clear();
}
void CObservable::SetChanged(){m_bChanged = true;
}
void CObservable::ClearChanged(){m_bChanged = false;
}
bool CObservable::HasChanged(){return m_bChanged;
}
int CObservable::GetObserversCount(){return m_setObs.size();
}
void CObservable::Notify(void* pArg /* = NULL */){if (!HasChanged()) return;cout << "notify observers…" << endl;ClearChanged();set<CObserver*>::iterator itr = m_setObs.begin();for (; itr != m_setObs.end(); itr++){(*itr)->Update(this, pArg);}
}
/具体应用类定义和实现
//bloger是发布者，即被观察者(subject)
class CBloger : public CObservable
{
public:void Publish(const string &strContent){cout << "bloger publish, content: " << strContent << endl;SetChanged();Notify(const_cast<char*>(strContent.c_str()));}
};
//portal是发布者，即被观察者(subject)
class CPortal : public CObservable
{
public:void Publish(const string &strContent){cout << "portal publish, content: " << strContent << endl;SetChanged();Notify(const_cast<char*>(strContent.c_str()));}
};
//RSS阅读器，观察者
class CRSSReader : public CObserver
{
public:CRSSReader(const string &strName) : m_strName(strName){}virtual void Update(CObservable* pObs, void* pArg = NULL){char* pContent = static_cast<char*>(pArg);//观察多个目标if (dynamic_cast<CBloger*>(pObs)){cout << m_strName << " updated from bloger, content: " << pContent << endl;}else if (dynamic_cast<CPortal*>(pObs)){cout << m_strName << " updated from portal, content: " << pContent << endl;}}
private:string m_strName;
};
//Mail阅读器，观察者
class CMailReader : public CObserver
{
public:CMailReader(const string &strName) : m_strName(strName){}virtual void Update(CObservable* pObs, void* pArg = NULL){char* pContent = static_cast<char*>(pArg);if (dynamic_cast<CBloger*>(pObs)){cout << m_strName << " updated from bloger, content: " << pContent << endl;}if (dynamic_cast<CPortal*>(pObs)){cout << m_strName << " updated from portal, content: " << pContent << endl;}}
private:string m_strName;
};
#include "observer.h"
int main()
{//目标(被观察者)CBloger* pBloger = new CBloger();CPortal* pPortal = new CPortal();//观察者. 一个观察者可以观察多个目标CRSSReader* pRssReader = new CRSSReader("rss reader");CMailReader* pMailReader = new CMailReader("mail reader");pBloger->Attach(pRssReader);  //bloger注册观察者pBloger->Attach(pMailReader); //bloger注册观察者pPortal->Attach(pRssReader);  //portal注册观察者pPortal->Attach(pMailReader); //portal注册观察者//博客发布信息pBloger->Publish("博客分享设计模式");cout << endl;//门户发布信息pPortal->Publish("门户分享设计模式");cout << "\nportal detached mail reader" << endl;pPortal->Detach(pMailReader);cout << "portal observers count: " << pPortal->GetObserversCount() << endl << endl;pPortal->Publish("门户分享设计模式");system("pause");return 0;
}